2. It sounds like you have already had a look at my faerie guide. There is a lot there to take in, but many of your questions are discussed in there. It may be worth going over it again later.
Specific to your question #2, they heal party members automatically within a range of 20y if below 80% health.
It is optimal to use manual commands to have her start casting embrace on the tank before his health drops to 80% to keep him topped off and/or buy a little more time before you have to heal him yourself.
Switching targets back and forth constantly to alternate between spamming Embrace and DPSing is an enormous pain in the butt, at least on PS3/4. I use macros for my attacks to make the process infinitely easier. I explained my macros for that purpose at the end of the guide.
3. I use targeting macros for my attacks for the reasons I outlined above. I also use several space saving macros.
Faeries still auto-heal on Steady mode. Faerie macros make it easier to control the faerie or make her more responsive to commands. Macros for faerie commands are not as necessary now as they were before 2.5. Pre-2.5, if you commanded your faerie to use an ability while she was casting embrace, she would simply ignore you. Since 2.5, faeries can queue a cooldown ability to use after embrace, but only if embrace was auto-cast, not manually cast. So macros used to be pretty necessary just for basic cooldowns to work but now are only sometimes needed.
5. Raminax nailed it with the picture. Figuring out which debuffs leeches actually works on, however, is not so easy.
6. Sacred soil is only good for group damage. That same aetherflow stack could have been used on lustrate for 25% of the tank's hp. In order for Sacred Soil to mitigate an equal amount of damage, the tank would have to take 250% of his health in damage over that 15 seconds.